Biota Babble

Editor's choice in immunology

By Edyta Zielinska | March 1, 2012

CROSSTALK: IgA producing B cells (green) appear in large numbers in the villi (purple) of the small intestine, where they help keep microbiota from suppressing metabolic functions of the epithelium (gray).Amiran Dzutsev & Natalia Shulzhenko

CROSSTALK: IgA producing B cells (green) appear in large numbers in the villi (purple) of the small intestine, where they help keep microbiota from suppressing metabolic functions of the epithelium (gray). AMIRAN DZUTSEV & NATALIA SHULZHENKO

The paper

The finding

Researchers show that three-way talk between the immune system, commensal bacteria and a third component, the intestinal epithelial cells is essential for normal gut function. Husband-and-wife first authors Natalia Shulzhenko and Andrey Morgun, working at the National Institute of Allergy and Infectious Diseases, found that when immune cells are absent or impaired, gut epithelial cells adopt a defensive stance toward the resident microbiota, at the expense of the epithelium's normal fat-absorbing functions.

The links

One of the most important immune cells in the gut is the B cell, which normally releases IgA antibodies into the intestine. Using mice that lacked B cells, the researchers noticed that a large number of genes involved in metabolism, especially in fat absorption, were transcribed less. But the effect disappeared when B-cell knockout mice were raised in germ-free conditions–i.e., when their guts lacked microbiota.

The concept

Normally, IgA crosses into the gut and controls or regulates the microbial population, says Shulzhenko. In the absence of B cells, the microbiota probably encroach into the gut's cellular lining, instigating a protective response. When the gut cells adopt this protective role, their metabolic and fat-absorbing functions are diminished.

The implication

This scenario may explain why immunocompromised "HIV patients and persons persistently challenged with multiple infections such as children in developing countries are prone to malnutrition/metabolic problems," says Andrew Gewirtz from Georgia State University.